Coated fabric insulation tape and process



Aug. 1, 1944.

K. H. BARNARD COATED FABRIC INSULATION TAPE AND PROCESS Filed Dec. 30, 1942 Patented Aug. l, 1944 Kenneth H. Barnard, Stamford, Conn., assignor to Pacific Mills, Boston, Mass., a corporation Massachusetts Application December 30, 1942, Serial No. 470,658

2 Claims. (eras-:14) This invention relates to bias cut insulation tape for use in wrapping cablejoints, coils and other irregularly-shaped electrical conductors, for insulating purposes.

Insulation tape of the type concerned is usually made of cotton fabric, such as print cloth, carded lawn, etc., which is coated with a suitable insulating varnish and cut longitudinally into tapes ready for use. It has been the practice to employ a fabric which is cut on the bias at an angle of approximately 45, that is, so that the warp and filling threads are each arranged at an angleof 45 to the length and width of the fabric and consequently are initially in the same angular position in tape strips cut longitudinally from the fabric.

It is an object of this invention to provide a novel and improved insulation tape which has desirable stretch characteristics. Another object is to provide such a tape which is more uniform in its stretch characteristics than prior tapes. An additional object-is to provide a stronger tape and one which has longer life than prior tapes.

I have discovered that if the fabric of the tape has its constituent threads so arranged that the warp and filling are not at the same angle to the edge of the tape, but one set of threads is at a lesser angle to said edge (i. e., more nearly parallel therewith), but still inclined thereto, an improved product is obtained. A preferred angle is approximately 30 to the length dimension of the tape. When one set ofthreads, for example the warp threads, is cut at an angle of 30 to the longitudinal edge of the tape, it will be seen that the-filling threads will lie initially at an angle of approximately 60 to the edge. These preferred angles may be varied, for example i-5. By this means, the properties of the tape for electrical insulating purposes are materially improved;

v Thus, the 30 or 60 cut tape will stretch substantially less longitudinally and somewhat more,

and lateral stretch characteristics than the conventional tapes. This is an important improvement.

The invention is illustrated in the accompanying drawing in which-- Fig. 1 shows a piece of cloth wo en with the threads. at right angles to one another;

Fig. 2 shows a strip cut from the piece of Fig. 1 with one set of threads, the filling, at an angle of 60 to the longitudinal line of the tape and the other,set of threads,,the warp, at an angle of 30;

Fig. 3 shows the strip stretched longitudinally so that the angle of the fillingis 50;

Fig. 4 is an enlarged diagram of the arrangethe finished tape showing the sets of threads I! and more easily laterally, than the cut tape I Thus the formation of air pockets is minimized or avoided. In addition, tapes having my construction are more uniform in their longitudinal as and n.

and M, thestarch l5 and the coatings of var- The tubular piece of cloth m, Fig. 1, is cut on an angle of 60 on the lines AB and CD, etc. The resulting strip M, Fig. 2, has one set of threads at an angle of about 60 to the longitudinal line of the tape and the other set of threads at right angles to the first set. In Fig. 4 the square a, b, c, (1, formed by the threads shown in Fig. 2, has its base at a and its apex at c offset from the line through a parallel to the longitudinal line of the tape- Y I have found that with the threads arranged as shown at H, Fig. 3, there remains in the tape the necessary capacity for further longitudinal 35 stretch, or residual stretch, but this residual stretch is so resisted by the set of threads 0, d and l, m, due to the relatively small angle, about 30", which they make with the longitudinal line of the tape, that further longitudinal stretch of the tape under variable longitudinal tension. which is applied in wrapping electrical conductors, is not so great as in the previously known and used tapes which have been cut at an angle of 45 to the longitudinal line of the tape. I have also found. that the stretch, even when subjected to different degrees of tension, is very much more uniform. At the same time Ihave retained in the stretched cloth very nearly the full area and width of the unstretched cloth so that the loss in area due tostretching is reduced to a very small percentage. I

The angle of the cut of the woven cloth may be varied so that one set of threads before stretching has an angle of' 60i5 and after stretching the angle becomes 5025", and the slight capacity of these threads for lengthwise stretching. As the construction of the invention also places the other set of threads more nearly in the direction of the width of the cloth than does the prior construction, it would seem, by parity of reasoning, that the widthwise stretchability of the tape of this invention would be less. Under longitudinal tension, however,

- which is necessarily applied in Wrapping a joint,

the reverse is true, possibly because the considerably greater lengthwise stretching of the prior art tape under these conditions has a correspondingly greater tendency to contract the tape widthwise which must be offset in order to produce any lateral stretch.

The fabric uesd for making tape according to this invention may be the same as that heretofore used for making insulating tape which has been, conventionally, a cotton print cloth counting 68 x '72 or 64 x 60, No. 39 to 41 filling thread and No. 28 to 30 warp thread, or a carded lawn '72 x 68, No. 36 to 40 warp and No.46 to 50 filling thread.

As an example of a suitable method for producing insulating tape according to the invention, I give the following:

A cotton cloth of suitable count and construction as above indicated is woven in the form of a tube. The fabric tube is singed inside and out and is then cut spirally from end to end, this cut being made on the bias atan angle of either approximately 30 or approximately 60 to its length and to its warp threads. This converts the tube into a single strip of fabric of substantially uniform width in which, if the cut was made at an angle of 30 to the warps, the warp threads lie at that angle, and the filling threads lie at an angle of 60 to the length of the strip, whereas if the cut was madeat a bias of 60 to the warps, the warp threads lie atthat angle, and the filling threads lie at an angle of 30, to the length of the strip. The width of this strip will, of course, depend upon the circumference of the fabric tube and the angle of cut. With a tube having a fiat width of about 40 inches, that is, a circumference of about 80 inches, a cut at a 60 bias to the warps will produce a strip having a suitable width of about 38 inches.

A convenient method for cutting the fabric tube in the above manner is as follows. The

- Woven tube is rolled up fiat on a roll which is rois 60", for example, the rolls, set at about that angle to the warps, will drive the tube around the surfaceof the cylinder by about twice the extent that they draw the tube down on the cylinder, the swivel suspension of the tube roll per-.

Consequently, a longitudinal pull exmitting this lateral, rotary motion of the tube about the cylinder, and the rotatable mounting of the roll permitting'the tube to unwind according to the downward pull of the drive wheels. As

it isthus driven about and along the surface of the cylinder, the tube is engaged by a cutting edge, for example a rotating carborundum wheel, set to make the cut at the predetermined angle to the warps.

Instead of cutting astrip of material for my novel tape from cloth woven in the form of a tube, pieces may be cut on the bias from straight cloth, these pieces being sewed together to form the so-called sewed bias material.

The bias cut fabric strip is now starched in a starch mangle, framed to finished width on a tenter, sprinkled and passed twice through a heavy friction hydraulic calender to give it a smooth finish on both sides. It is then wound. up and run through a varnish tower which applies a coating of a suitable electrically insulating varnish to both sides of the strip. The strip is dried and then cut longitudinally into tapes from inch to 2 inches wide which are wound on spools, ready for use.

Due to stresses occurring in the process of manufacture, the angulararrangement of the warp and filling threads, both with regard to that one set of threads originally is at an angle of 30 and the other at an angle of 60 to the length of the tape, the 30 threads tend to remain at an angle of 3015 to the length of the tape, in the final product, but the angle of the 60 threads tends to decrease and is likely to be around 50:5.

This is in rather marked contrast to the effect obtained in processing the prior art 45 cut tape. In this tape, the angle of both sets of threads to the length dimension of the fabric shows a slight tendency to decrease, for example of the order of 5 more or less, so that in the final tape both sets of threads tend in general to run at an angle of 40 to 45 to the length of the tape.

In my novel product, however, the 40 threads tend to retain their angle with the length dimension of the tape, while the corresponding angle of the 60 threads tends to decrease to a substantially greater extent than is the case with the 45 cut.

Fig. 2 shows my tape before it is stretched by the stresses occurring in the process'of manufacture and Fig. 3 shows this tape so stretched. As shown in Fig. 4, the square a, b, c, d, is an enlargement of the small squares shown in Fig. 2 and the rhombus a, l, m, d is an enlargement of the small rhombi shown in Fig. 8. It is obvious that the area of any portion of the'stretched tape is less but not substantially less than the area of the same portion before stretching. Specifically, as shown in Fig. 4, the dimensions of the square and the rhombus are such that the area of the rhombus is approximately 98% of the area of the square. I

Having now described preferred embodiments of the invention, what I desire to claim and secure by Letters Patent is:

1. An insulating fabric tape for wrapping irregularly shaped electrical conductors, said tape being composed of a set of warp threads and aan angle of approximately 30 being disposed at to the longitudinal line of the plus or minus 5 tape and the other of said sets of threads being disposed at an angle of approximately 50 plus or minus 5 to said line and said tape having the area of any portion composed of a given number of warp' and filling threads not substantially less than the area of the same portion with the same threads at right angles to each other, and a threads, cutting said tube helically' at an angl of 60:5 to the threads of one of said sets and at an angle of about 30 to the threads of the other of said sets to form strips, processing a strip to dispose the first-named set of threads at an angle of 50i5 to the longitudinal line of said strip and to dispose the second-named set of threads at an angle of not over 30 to said longitudinal line while maintaining the area. of said strip not substantially less than its area before processing, and then coating said strip with insulating varnish.

KENNETH H. BARNARD.

CERTIFICATE OF .00 RREC TI ON 0 Patent No. 2, ,0 8. August 1-, 19th:

KENNETH H BARNARD It is hereby certified that error appears in the printed specification of the above numbered patent requiring correctionae follows: Page 2, first column, line 26, for "need" read --used-; and second column, 11neh9,for "ho read --5o--; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5th day of September, A. D. -l9l l4..

Leslie Frazer (Seal) Acting Commissioner of Patents. 

